The introduction of molecular sieve-type cracking catalysts resulted in a dramatic improvement in cracking activity and selectivity of the catalyst. The sieves were found to have intrinsic activity for cracking far greater than the conventional silica-alumina cracking catalysts that were in use at the time of the introduction of the molecular sieve-type catalyst.
There are several patents describing processes for the preparation of these zeolites. U.S. Pat. No. 3,692,665, for example, covers a method for preparing a faujasite type zeolite that is stabilized by cation and thermal stabilization. The older more conventional cracking catalysts are described in patents such as U.S. Pat. No. 3,404,097 to Wilson et al. which describes a silica magnesia fluoride catalyst. U.S. Pat. No. 3,650,988 of Magee et al. covers a process for preparing a hydrocarbon cracking catalyst containing a semi-synthetic portion, i.e., clay, silica-alumina and a zeolite portion. There are several other patents describing processes for preparing molecular sieve-type catalysts. U.S. Pat. No. 3,425,956 of Baker et al. is typical of a large body of art in this area.
Copending application Ser. No. 423,637 of Elliott filed Dec. 10, 1973, now U.S. Pat. No. 3,867,308 describes a process for preparing a cracking catalyst by preparing a hydrosol by rapid addition of mineral acid to sodium silicate, adjusting the pH of the sol, adding clay and zeolitic components, spray drying, washing with water, rare earth exchanging and recovering the product. The instant case process is an improvement over this process, in that it affords much better control of the pH during the catalyst preparation and minimize problems that might arise due to gelling of the silica hydrosol in the equipment during the processing.